The aircraft flight data recorder (FDR) is a device that preserves the recent history of an aircraft flight through the recording of dozens of parameters collected several times per second. The aircraft cockpit voice recorder (CVR) preserves the recent history of the sounds in the cockpit including the conversation of the pilots. The two recorders give an accurate testimony narrating the aircraft's flight history to assist in any later investigation. Modern FDRs are typically protected from crash damage by a double wrap of strong corrosion-resistant stainless steel, or titanium, on the exterior and high-temperature insulation inside for protection against fire. An underwater locator beacon transmitter (i.e., pinger) is mounted on a bracket bolted to the front of an FDR, designed to emit an ultrasonic “ping” for up to 30 days and enable operation while immersed to a depth of up to 6,000 meters (20,000 ft.). Together, these recorders are known as “black boxes”.
The sea is a difficult search environment and technology limitations are problematic. Black boxes are often hard to locate when an aircraft goes down over water and much more difficult to locate when the aircraft goes down over deep water. Existing search methods involve manual efforts that can be dangerous, costly, time consuming, and highly dependent on good weather conditions. If the crash site is not found immediately, water currents can disperse crash debris over hundreds of miles. The ultrasonic pinger (i.e., Underwater Locator Beacon, “ULB”) in the FDR has a finite battery life (30 days) and limited detection range (1 to 2 kilometers under normal conditions). Crash sites in deeper water make locating the black boxes even more difficult because of high pressures and the presence of inversion layers (i.e., layers of different water temperatures and salinity that create acoustic boundaries). These layers of deep alternating water densities can reflect and scatter the pinger sound obscuring it. Such effects can combine to give a false location or make the pinger completely undetectable and prevent the ULB from being found. Further, ocean noise competes with the ULB and can mask the pings or create false ping detections.
Oceans cover about 71% of the Earth's surface, 90% of which is considered deep ocean (i.e., more than 200 meters deep). The deepest part of the ocean called the Abyssopelagic Zone (or Abyssal Zone) is over 4,000 meters deep and occupies 83% of the oceans' total area (about 300 million square kilometers). Each of the oceans has its own average depth, from the relatively shallow Arctic Ocean at 1,200 meters to the Pacific Ocean at 4,638 meters. Deep trenches are found in all oceans and the Marianas Trench is believed to be the deepest at 11,021 meters.
The ULB is detectable under normal conditions over a range of 1-2 km, and under good conditions up to 4-5 km. It is activated by immersion in water. The frequency of the pings is 37.5 KHz (±1 kHz) with an acoustic output of 160.5 db. The pulse rate is 0.9 pings per second. The power source is a lithium battery.
Existing beacon locator technology in use today is boat towed, manually deployed, and requires the use of: a towed detector, tow cables, winches, hydraulic power units, generators, and an operator at a control console on the tow boat to monitor the system for detections. Such systems have limited capabilities and coverage and can only be safely and effectively used under good weather conditions.
Some representative aircraft ocean crashes include TWA Flight 800 in 1996. The black boxes were found in 8 days, at a depth of 37 meters. The black boxes for Egypt Air 990 in 1999 were found after 10 days at a depth of 60 to 83 meters. The black boxes for Air France Flight 447 were found in May 2011 at a depth of 2,987 meters after a search of about 700 days, long after the pinger battery expired. Malaysia Air Flight 370 is still an ongoing search, at depths of about 3,900 meters. It would be desirable to have a device that could search autonomously within a search grid and that: does not require a towing vessel, is surface and air deployable, is able to search at all ocean depths under all sea and weather conditions, requires no human participation on site, and is capable of regularly sending search reports from anywhere in the world to a stationary, or mobile, search coordinating facility anywhere in the world.